The present invention relates to level measurement systems, and more particularly to a power saving method and system for the analog-to-digital converter stage in pulse-echo acoustic ranging and time of flight ranging systems.
Pulse-echo acoustic ranging systems, also known as time of flight ranging systems, are commonly used in level measurement applications. Pulse-echo acoustic ranging systems determine the distance to a reflector (i.e. reflective surface) by measuring how long after transmission of a burst of energy pulses the echo is received. Such systems typically use ultrasonic pulses or pulse radar signals. In applications for time of flight pulse-echo acoustic ranging systems, there are power supply limitations necessitating that these instruments operate from very small amounts of current.
The current loop configuration is one well-known approach to the power supply limitations imposed on pulse-echo ranging systems or time of flight distance ranging systems. For the current loop configuration, the instrument must consume between 4 mA and 20 mA both to power itself and to indicate the distance measured.
As a result of the constraints of the current loop configuration, various schemes have been devised to reduce the power consumed by these instruments. One scheme involves putting the microprocessor into a xe2x80x98sleepxe2x80x99 or xe2x80x98idlexe2x80x99 state between measurements. Another scheme involves only running various parts of the system when required and then switching them off when not required.
A further requirement for more sophisticated time of flight ranging systems and pulse-echo acoustic ranging systems is the need to process the entire received echo waveform in order to extract the correct echo. It is necessary to process the entire received waveform to separate the echo from the clutter of other signals which may appear in the waveform. In such systems, the received echo waveform is digitized using an analog-to-digital (A/D) converter and the converted waveform is stored for subsequent processing.
The resolution of the distance measurement is related to the rate at which the received echo waveform is sampled by the A/D converter. The received echo waveform is also known as the echo profile in time of flight ranging. If the received echo waveform or profile is sampled more rapidly, then there will be more points per unit length than there would be if a slower sample rate were utilized. It will be appreciated that the accuracy of the distance determination or level measurement is improved by a higher sampling rate of the received echo waveform or profile. Unfortunately, faster sample rates mean higher power consumption.
To alleviate the concomitant power consumption penalty associated with the higher sampling rates, a number of approaches have been attempted. If the sample rate is reduced, then the A/D converter will consume less power. One approach involves turning off the A/D converter, or switching to a lower power mode, when an echo profile is not being sampled. Another approach involves utilizing a slower A/D converter which consumes less power than the faster sampling A/D converters. Other power saving approaches involve saving power in the operation of the central processing unit (CPU) which controls the operation of the A/D converter and the pulse-echo acoustic ranging system. The CPU is turned off between conversions of the received echo waveforms or the CPU is run more slowly. A slower low power CPU may also be utilized to control the pulse-echo acoustic ranging system. For implementations where a single chip microcontroller unit (MCU) is utilized with a built-in, on-chip, A/D converter, the design choice is to select a low power MCU.
While the known approaches can decrease power consumption in time of flight ranging devices and pulse-echo acoustic ranging systems, there is still room for improvement. Accordingly, there remains a need for improvement in power consumption in time of flight ranging devices and pulse-echo acoustic ranging systems.
The present invention provides a mechanism for reducing power consumption in an analog-to-digital converter without incurring the usual penalty related to loss of resolution.
In a first aspect, the present invention provides a method for converting a received echo signal into a digital form suitable for further processing in a time of flight ranging system, the method includes the steps of: (a) inputting the received echo signal, said received echo signal having a signal envelope; (b) sampling the signal envelope of the received echo signal at precise intervals to obtain amplitude measurement points for the received echo signal; and (c) applying an interpolation function between each pair of adjacent amplitude measurement points, the interpolation function provides a closer approximation of the shape of the received echo signal envelope.
In another aspect, the present invention provides a time of flight ranging system having: (a) a transducer for emitting energy pulses and coupling reflected energy pulses; (b) a controller having a receiver component and a transmitter component, and the controller including an analog-to-digital converter and a precise time-base generator; (c) the transducer having an input port operatively coupled to the transmitter component which is responsive to the transmitter component for emitting the energy pulses, and the transducer includes an output port operatively coupled to the receiver component for outputting reflected energy pulses coupled by the transducer; (d) the receiver component converts the reflected energy pulses into corresponding electrical signals, and the receiver component includes an output port coupled to an input port on the analog-to-digital converter which receives the electrical signals, the analog-to-digital converter is responsive to control signals from the controller for obtaining amplitude measurement points at predetermined intervals derived from the precise timebase generator; (e) the controller includes a program component for applying an interpolation function between adjacent amplitude measurement points, and the interpolation function provides an approximation of the reflected energy pulse shape between the adjacent amplitude measurement points.
In a further aspect, the present invention provides a pulse-echo acoustic ranging system comprising: (a) a transducer for emitting acoustic pulses and detecting reflected acoustic pulses; (b) a controller having a receiver component and a transmitter component, and the controller including an analog-to-digital converter and a precise timebase generator; (c) the transducer has an input port operatively coupled to the transmitter component and is responsive to the transmitter component for emitting the acoustic pulses, and the transducer includes an output port operatively coupled to the receiver component for outputting reflected acoustic pulses coupled by the transducer; (d) the receiver component converts the reflected acoustic pulses into corresponding electrical signals, and the receiver component has an output port coupled to an input port on the analog-to-digital converter for receiving the electrical signals, the analog-to-digital converter is responsive to control signals from the controller for obtaining a plurality of amplitude measurement points at predetermined intervals derived from the precise timebase generator; (e) the controller includes a program component for applying an interpolation function between adjacent amplitude measurement points, and the interpolation function provides an approximation of the reflected acoustic pulse shape between the adjacent amplitude measurement points.